Characterization of ALD Ta₂O₅, Al₂O₃, and Ta₂O₅/Al₂O₃ Nanolaminate as Metal-Insulator-Metal Capacitor Dielectric for GaAs HBT Technology

Abstract

Tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and Ta2O5/Al2O3 nanolaminate deposited using atomic layer deposition (ALD) have been characterized and evaluated as metal-insulator-metal (MIM) capacitor dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. The results show that the capacitor with 60 nm of ALD Ta2O5 and Al2O3 capacitor dielectric films resulted in a capacitance density of 3.84x10-15 F/μm2 and 1.37x10-15 F/μm2 and a dielectric constant of 26.1 and 9.3, respectively, while the capacitor with 60 nm of ALD Ta2O5/Al2O3 nanolaminate capacitor dielectric film resulted in capacitance density of 2.40x10-15 F/μm2 and a dielectric constant of 16.3. The capacitance density of capacitor using these three films increased marginally by 2.2% to 4.3%, when the temperature was increased from 25oC to 125oC. No significant change in capacitance density of these ALD films was observed, when the applied voltage was varied from -5 V to +5 V. The leakage current density of the ALD Al2O3, Ta2O5, and Ta2O5/Al2O3 nanolaminate films at an electric field of 3 MV/cm is 2.0x10-16 A/μm2, 6.8x10-8 A/μm2, and 9.2x10-13 A/μm2, respectively. The 60 nm ALD Al2O3 film has higher breakdown voltage of 46 V, compared to the 60 nm ALD Ta2O5 film and the 60 nm Ta2O5/Al2O3 nanolaminate film, which has a breakdown voltage of 22.5 V and 32.7 V, respectively. As the temperature was increased from 25oC to 125oC, the leakage current increased and breakdown voltage decreased for all three ALD films.